Development of Iron Phosphate Wasteforms for Fission Products Waste Streams

Most liquid high-level nuclear waste is currently being immobilized to a solid form as a borosilicate glass by vitrification. However, many nuclear wastes have complex and diverse chemical compositions that reduce their compatibility with borosilicate glass. The current baseline spent nuclear fuel reprocess generates secondary waste streams that generally include large amounts of MoO3 and lanthanides that are poorly soluble in borosilicate glasses and thereby limit the waste loading. New waste forms as alternatives to borosilicate glass are being sought to increase the waste loading while retaining acceptable chemical durability and thus to decrease the total nuclear waste volume required for storage and disposal. The main goal of the proposed nine month, SBIR Phase I program is to develop suitable iron phosphate-based compositions for vitrifying the MoO3-rich waste generated from reprocessed spent nuclear fuel with greater waste loadings than can presently be achieved with borosilicate glass and while retaining chemical durability that meets or exceeds appropriate DOE standards. Our previous studies have already demonstrated proof-of- concept for molybdenum solubility in an iron phosphate glass. During the Phase I program, we will formulate iron phosphate compositions to develop advanced waste forms, which can contain larger amounts ( & gt;40 wt%) of the MoO3-rich waste, compared to a borosilicate glass, while demonstrating (1) a good glass forming tendency, (2) moderate/practical melting and forming temperatures ( & lt;1200C), and (3) acceptable waste form properties, especially a chemical durability meeting the Product Consistency Test (PCT) requirements. Commercial Applications and Other Benefits: The proposed research will demonstrate that iron phosphate waste forms will increase radioactivity concentrations that can be safely stored and thereby decrease the total nuclear waste volume for storage and disposal. This would lead to considerable savings of time and money for the Nations effort related to nuclear waste remediation, something that is especially needed for the advanced domestic fuel cycle program.